OBJECTIVES: (1) To search for viruses which may play an etiological role in the syndrome of acute infectious nonbacterial gastroenteritis of infants, children, and adults. (2) to cultivate (in vitro) the viral agent(s) of acute infectious nonbacterial gastroenteritis; (3) to study the biophysical, immunological, and epidemiological characteristics of such agent(s); (4) to reproduce the syndrome experimentally in volunteers for the purpose of a) studying the pathophysiological and immunological responses of the host, and b) assaying the infectivity of such viral agents; (5) to develop effective immunoprophylaxis for the viruses of acute, infectious, non-bacterial gastroenteritis.